The invention relates to a print control apparatus and its print control method and, more particularly, to an error recovery system of a paper jam error or the like occurring in a shuttle printer or a page printer such as a laser printer, an LED (Light Emitting Diode) printer, an LCS (Liquid Crystal Shutter) printer, or the like.
Hitherto, an disclosed in JP-A-60-257262 (hereinafter, referred to as a first prior art), a printer has command buffers of the number as many as commands of the maximum number of sheets (hereinafter, simply referred to as a maximum holding number) which can be simultaneously print processed in the printer, in which each command buffer is used to hold a print command transmitted from a host computer until the completion of the paper discharge as a normal end of the printing process of the print command. When an error such as a paper jam or the like which needs the reprint occurs, causes of the error are eliminated and then the print command after the time point of the occurrence of the error is read out from the command buffer and the print is again executed and the error recovery is performed.
In JP-A-3-155974 (hereinafter, referred to as a second prior art), when an error such as a paper jam or the like occurs in a printer, the printer notifies the kind of error occurring in a host computer and the page in which such an error has occurred. The host computer which has received such a notification again transmits a print command after the page having the error to the printer for the error which needs the reprint, thereby enabling the printer to reprint the pages after the error occurring portion.
In JP-A-3-224778 (hereinafter, referred to as a third prior art), when an error such as paper jam or the like occurs in a printer, the printer notifies the kind of error which has occurred in a host computer, the host computer which has received such a notification again transmits the print command train after the head page constructing a document for the error which needs the reprint.
For such a retransmitted print command train, the printer executes the following processes with regard to the pages before the page having the error.
(1) When a command is determined to be a setting command of attribute parameters by a command interpretation, the command is executed, so that the attribute parameters are set into a table called an attribute parameter table. The attribute parameters include a paper size, a line pitch, a character pitch, a character kind, a character size, a line type, and the like.
(2) However, when the command is for drawing a character, a figure (straight line, arc, circle, polygon, or the like), an image, or the like, the command is not executed.
(3) The printing process about the page buffer is not activated as well.
With respect to the pages after the page in which the error has occurred, the printer executes both of the image drawing process and the printing process in the ordinary manner.
According to the above first prior art, for instance, in a laser printer having a printing speed of 20 sheets/min, the papers in a range from about ten to twenty sheets are substantially simultaneously concerned with the printing process, so that the maximum holding number lies within a range from about 10 to 20. A capacity of the print command per paper is equal to about two Mbytes in case of transmitting the image of one page of the A4 size as image data of a density of 400 dots/inch. Therefore, in this case, a memory of at least about 20 to 40 Mbytes is necessary as a special command buffer only for use of the error recovery mentioned above, so that there is a problem such that the costs remarkably increase. According to the first prior art, nothing is considered with respect to a point that the drawing attribute parameters are handed over between the pages. Therefore, even if the print command is preserved, in case of performing the error recovery using the preserved print command from the page having the error as a start page, the attribute parameters until the error occurring page are not handed over, so that there is also a problem such that the result of the reprint from the error occurring page cannot be printed as an original page by the attribute parameters before the occurrence of the error.
According to the second prior art, when the reprint is executed, the host computer again transmits the print command train after the error occurring page to the printer. However, even when the host computer again transmits the print command train after the error occurring page, the values of the attribute parameters which have been set and updated by the print command train before the error occurring page cannot be recognized by only the retransmitted print command train, so that there is a problem such that the inherent print by the attribute parameters before the error occurs cannot be performed.
According to the third prior art, with respect to the page before the error occurring page, the printer interprets the command as mentioned above and, in case of the setting command of the attribute parameters, the printer executes such a setting command and doesn't execute the command to draw an image and the printing process. Such a processing method is hereinafter called a command read skipping process. Such a command read skipping process is a complicated process. That is, when a plurality of printer escape sequence commands which are peculiar to the respective companies and a plurality of page describing languages such as Post Script (registered trade name of Adobe Systems Co., Ltd.) and Interpress (registered trade name of Xrox Co., Ltd.) are supported as various kinds of drawing commands, it is necessary to execute such a read skipping process with respect to each of various kinds of drawing commands, so that there is a problem such that a development program amount increases.
The above problems are large subjects in, particularly, a print control apparatus which executes the drawing process and the printing process as a multi task construction in a concurrent or parallel manner.